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A.'BARR AND W. STROUD. s'eLF'coNrA'INEo BASE SINGLE OBSERVER HEIGHI MEASURING INSTRUMENT OF THE RANGE FINDER TYPE. 1 APPLICATION FILED MAR. 26. I919- 1,312,014. Patented Aug. 5,1919.

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A. BARR AND W. STROUD.

SELF CONTAINED BASE SINGLE OBSERVER HEIGHT MEASURING INSTRUMENT OF THE RANGE FINDER TYPE.

APPLICATION FILED MAR. 26, 1919.

"1,312,014. 7 Patented Aug. 5, 1919.

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M 1 N N N FIGIIO 0 AneHInALn BARB. Ann WILLIAM STROUID, or ANNIESLALND, GLASGOW, SCOTLAND.

SELF-CONTAINED BASE SINGLE-OBSERVER HEIGHT-MEA RANGE-FINDER TYPE.

, Specification of Letters Patent. P t t d (1 ;5,1919

Application filed. March 26,1919. Serial 1a. 285.370.

To all whom it may concern:

Be .it known that we, Ancnrnann BARR and WILLIAM S'rnoUD, subjects of the King of Great Britain and Ireland, and both of Caxton street, Anniesland, Glasgow, Scotland, have invented newv and useful Tmprovements in Self-Contained Base Single- Observer Height-Measuring Instruments of the Range-Finder Type, of which the following is a specification.

This invention reters to self-contained base single-observer hei ht measuring instruments of the range-linder type having a double telescope system and associated eyepiece system in each telescope of which a retracting prism of small angle is provided capable of translation along the axis ofits telescope in the beam of light which passes from the objective to the eyepiece system (for measurements appertaining to ranges, and for measurements appertaining to heights is so arranged that the angle which the principal plane of refraction of the prism makes with the plane of triangulation varies in such a manner as to be always equal to the angle between the line of sight and the vertical. In operating the instrument the two prisms are moved simultaneously toward or from the eyepiecesystem. The general principle upon which instru: ments of this description operate for meas uring, heights is known and maybe ex plained by considering the conditions appertaining to an instrument which forvaymg angles of sight is mounted capableof rota tion about a horizontal axis containin the base of triangulation. In this case, il the retracting prisms are arranged so that the principal plane of refraction is maintained always in the plane of triangulatlon and adjustment of the prisms provided for each along the axis of its telescope only, ranges are always obtained for all angles of-slght, and when used on a target in the zenith the principal plane of refractiouis vertical, heights and ranges in this positlon being synonymous. If, however, provision is made for maintaining the principal plane of refraction always vertical, then, whatever the angle of sight, the indications obtained will be heights instead of ranges.

With instruments of this description working upon the coincidence or stereoscopic princip1e, the positlon of the retracting prisms for infinite height theoretleally is at the common focal plane of the two telescopic objectives which would normall be on the eye side of the reflecting faces oi: the eyepiece system. Under these onditions it is not possible to translate the retracting prisms to the position corresponding to infinite height, a requirement which is desirable for various reasons, one of which being that the setting of the scale reading of the instrument may thereby be readily tested. Moreover, owin to the size of the prisms comprised in the eyepiece system it is not possible to bring the retracting prisms any where near the infinity position which means that the heights measurable are of very restricted magnitude.

For angles of sight varying from 0 to 90 the instrument may be mounted capable of rotation about a horizontalaxis containing the base of triangulation, in which case the retracting prisms may each be suspended pendulum-wise so as to swing under gravity about an axis parallel to {the base of the instrument, in which case the principal plane of refraction will be always vertical, or the instrument may be mounted capable of rotation about a horizontal axis at right angles to the base of triangulatiomin which case the prisms may each be mounted in a carrier associated with gearing whereby the prism is turned about the axis of the base in the process ofturning the range finder about the horizontal axis for varying angles of sight. This method may, if desired, be adopted in the former case instead of the pendulum system of control.

The object of this invention, which refers to instruments of the rangefinder type comprising retracting prisms adapted to operate in themanner described, is to provide means in the double telescope system whereby a condition corresponding to measurements appertaining to infinite height may be established.

According to thisinvention there is provided in one or in each of the telescopes oi the double telescope system an auxiliary prism by which deviation equal to or slightly greater or less than that obtained by the two refracting prisms of the telescopes is produced, the auxiliary prism or each of them being fixed so far as translation along the axis of the telescope is concerned but being arranged to be rotated with varying angles of sight in the same SURING nsrnnivrmvror THE way and to the same extent as the two refracting prisms, the disposition of a refracting prism and its associated auxiliary prism being such that at the infinity position the refraction produced by the one is annulled by that of the other.

Some examples according to this invention applied to instruments of the rangefinder type working on the coincidence principle will now be described with reference to the accompanying drawings, in which Figure 1 is a plan of a height measuring instrument, Fig. 2 is a sectional end elevation illustrating a part thereof, and Flg. 3 is a sectionalside elevation illustrating a detail of Fig 2..

Fig. 4 is a sectional end elevation corresponding to Fig. 2 illustrating a modification.

Fig. 5 is an elevation illustrating a modifiedform of instrument and Fig. 6 is a side view of a part thereof.

Figs. 7, 8, 9 and 10 are plan diagrams illustrating the double telescope system of an instrument embodying modifications according to this invention.

The instrument illustrated at Figs. 1 and 2 is adapted to be rotated about a horizon tal axis X X for varying angles of sight. In this construction A A designate the end reflectors, B B the objectives, C the eyepiece system, which, for simplicity, is illustrated diagrammatically as though it consisted of single plane-reflectors, and D D designate the refracting prisms which are adapted to be moved to and fro along the axis X X for measurements appertaining to ranges, for which purpose each prism D is attached to a support, L mounted on a screw shaft N. For measurements appertaining to heights, each prism D is mounted on its support L to'swing pendulum-wise about a pivot E, see Figs.- 2 and 3, the axes of the pivots E being parallel to the axis X X, so that the effective angle of refraction of each prism D in the plane of triangulation alters in correct proportion to the angle of sight as the instrument is directed upon a target, say, an aircraft. In this case the refracting edge will always remain horizontal, i. 0., the principal plane of refraction of each prism D will be maintained vertical.

Themodification illustrated at Fig. 4 represents an instrument supported with its axis horizontal as in Fig. 1, but with its plane of triangulation directed at 45 to the horizontal plane, the eyepiece C ofthe eyepiece system being so arranged that in this position observations are made by looking down perpendicularly, to the plane of triangulation, a method which is frequently adopted in rangefinders for'observations on aircraft.-

The instrument illustrated at Fig. 5 is adapted to be irotated about a horizontal axis X X at right angles to the plane of triangulation for varying angles of sight. The end reflectors A A, objectives B D, the eyepiece system C, are arranged as indicated in Fig. 1, but, in this case, the refracting prisms D D, which are adapted to be moved to and fro along the axis of the instrument, are each mounted in a carrier F and rotatable about the axis of the instrument as the angle of sight is varied in the process of directing the instrument. For these purposes gear may be provided as shown, consisting of a helical wheel G fixed to its shaft which may be controlled in position by a pendulum with a heavy bob so that as the angle of sight of the instrument is varied by rotation about the axis X X the wheel G remains stationary. Gearing with G is a helical wheel H fixed to a shaft H to which two long pinions K are fixed, one on each side of the wheel H. In mesh with each pinion K is a gear wheel F formed in a part with the carrier F within which the refracting prism D is mounted, the carrier F being mounted to rotate in a support L mounted upon a screw shaft N by which each support L and with it each carrier F and prism D is adapted to be moved to and fro along the axis of the instrument according to varying range, and for measurements of height rotated as the instrument is turned about the horizontal axis X X by the operation of the helical wheel H, which is caused to rotate as it revolves about the helical wheel G, transmitting its motion by the shaft II to each of the long pinions K which thus turns each gear wheel F and with it its carrier F and prism D.

According to this invention the instruments illustrated at Figs. 1 and I are each provided with auxiliary prisms D ,D as shown in the diagram, Fig. 7. In this case D D are auxiliary prisms having equal angles of refraction each being equal to or slightly greater than the angle of refraction of the refracting prisms D D which themselves are equal. The auxiliary prisms D D are not translatable along the axis of the instrument, whereas the refracting prisms D D are, but all the prisms D D D D are similarly mounted so that the angle which the principal plane of refraction of each prism makes with the plane of triangulation varies equally in accordance with the angle of sight at which the instrument is directed, the extent and direction of angu' lar movement, relative to the plane of triangulation being equal for each prism. With this arrangement, when the refracting prisms D D are each in contact or there about with their associated auxiliary prisms D D respectively, the auxiliary prisn'is D D anul the effects of the refracti'ng prisms D D and. there is thus established an infinity condition the position of which has virtually been shifted from the eye side of the eyepiece system to the objective side thereot, in this case to the position occupied by the auxiliary prisms D D.

In the modification illustrated at Fig. 8, one auxiliary prism D is provided in one ot the telescopes only. In this case the angle of retraction of the prism D is double or approximatelydouble that of its associated retracting prism D. This prism may, as shown, be placed in the position occupied by one ot the auxiliary prisms D Fig. 3.

A modification ot the arrangement shown at Fig. 7 is illustrated at Fig. 9. In this case the auxiliary prisms D D are placed each between its associated objective B and retracting prism D. In this case the infinity position is near the objective and the retracting angle ,ot each auxiliary prism D is equal to or slightly less than that ot its associated retracting prism D. A similar modification ot the arrangement shown at Fig. 8 is illustrated at Fig. 10. In this case the auxiliary prism D is placed between its associated objective and retracting prism D.

We claim:

1. A self-contained base single-observer height measuring instrument ot the rangefinder type having a double telescope system and associated eyepiece system, a retracting prism in each telescope, means tor translating each retracting prism along the axis of its telescope, an auxiliary prism provided in one ot the telescopes fixed at a position on the axis of the telescope with which it is as sociated, by which deviation equal to or slightly greater or less than that obtained by the two retracting prisms ot the telescopes is produced, and means whereby each retracting prism and the auxiliary prism is so maintained that the angle which its principal plane 0t retraction makes with the plane ot triangulation varies in such a manner as to be always equal. to the angle between the line of sight and the vertical tor the purposes set forth.

2. A self-contained base single-observer height measuring instrument of the range finder type having a double telescope system and associated eyepiece system, a retracting prism in each telescope, means tor translating each retracting prism along the axis ot its telescope, two auxiliary prisms one in each ot the telescopes, each fixed at a position on the axis of the telescope with which it is associated, by which deviation equal to or slightly greater or less than that obtained by the two retracting prisms ot the telescopes is produced, and means whereby each retracting prism and each auxiliary prism is so maintained that the angle which its principal plane of retraction makes with the plane of triangulation varies in such a manner as to be always equal to the angle between the line ot sight and the vertical, tor the purposes set torth.

3. A selt-contained base single-observer height measuring instrument of the range; finder type having a double telescope system and associated eyepiece system, a retracting prism in each telescope, means tor translating each retracting prism along the axis of its telescope, an auxiliary prism provided in one of the telescopes fixed at a position between the eyepiece system and retracting prism on the axis of the telescope with which it is associated, by which deviation equal to or slightly greater than that ob tained by the two retracting prisms ot the telescopes is produced, and means whereby each retracting prism and the auxiliary prism is so malntained that the angle which its principal plane of refraction makes with the plane ot triangulation varies in such a manner as to be always equal to the angle between the line of sight and the vertical, tor the purposes set forth.

a. A self-contained base single-observer height measuring instrument ot the rangefinder type having a double telescope system and associated eyepiece system, a, re tracting prism in each telescope, means for translating each retracting prism along the axisot its telescope, two auxiliary prisms, one in each of the telescopes, each fixed at a position between the eyepiece system and retracting prism on the axis of the telescope with which it is associated, by which deviation equal to or slightly greater than that obtained by the two retracting prisms ot the telescopes is produced, and means whereby each retracting prism and each auxiliary prism is so maintained that the angle which its principal plane of retraction makes with the plane at triangulation varies in such a manner as to be always equal to the angle between the line of sight and the vertical, tor the purposes set forth.

5. A selt-contained base single-observer height measuring instrument of the rangefinder type having a double telescope system and associated eyepiece system, a retracting prism in each telescope, means tor translating each retracting prism along the axis of its telescope, an auxiliary prism provided in one of the telescopes fixed at a position on the axis of the telescope with which it is associated, by which deviation equal to or slightly greater or less than that obtained by the two retracting prisms ot the telescopes is produced, and gear mechanism for each prism whereby each retracting prism and the auxiliary prism is so maintained that the angle which its principal plane of retraction makes with the plane ot triangulation varies in such a manner as to be all ways equal to the angle between the line 0t gighlti. and the vertical, tor the purposes set ort 1 6. A self-contained base single-observer height measuring instrument of the rangefinder type having a double telescope system and associated eyepiece system, a retracting prism in each telescope, means for translating each refracting prism along the axis of its telescope,'two auxiliary prisms one in each of the telescopes, each fixed at a position on the axis of the telescope with which it is associated, by which deviation equal to or slightly greater or less than that obtained by the two refracting prisms of the telescopes is produced, and gear mechanism for each prism whereby each retracting prism and each auxiliary prism is so maintained that the angle which its principal plane of refraction makes with the plane of triangulation varies in such a manner as to be always equal to the angle between the line of sight and the vertical, for the purposes set forth.

7 A self-contained base single-observer height measuring instrument of the rangefinder type having a double telescope system and associated eyepiece system, a refracting prism in each telescope, means for translating each refracting prism along the axis of its telescope, an auxiliary prism provided in one of the telescopes fixed at a position between the eyepiece system and retracting prism on the axis of the telescope with which it is associated, by which deviation equal to or slightly greater than that obtained by the two retracting prisms of the telescopes is produced, and gear mechanism for each prism whereby each refracting prism and the auxiliary prism is so maintained that the angle which its principal plane of refraction makes with the plane of triangulation varies in such a manner as to be always equal to the angle between the line of sight and the vertical, for the purposes set forth.

8. A self-contained base single-observer height measuring instrument of the rangefinder type having a double telescope system and associated eyepiece system, a retracting prism in each telescope, means for translating each retracting prism along the axis of its telescope, two auxiliary prisms, one in each of the telescopes, each fixed at a position between the eyepiece system and re fracting prism on the axis of the telescope poses set forth.

ARCHIBALD BARR. WILLIAM STROUD.

V Copienefothie patent may be obtained for five cents each, by addressing the Commissioner of latents,

Washington, D. G. 

